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Re: [Qemu-ppc] [PATCH v1] target/ppc: rewrite f[n]m[add, sub] using floa

From: Richard Henderson
Subject: Re: [Qemu-ppc] [PATCH v1] target/ppc: rewrite f[n]m[add, sub] using float64_muladd
Date: Thu, 2 Mar 2017 13:22:05 +1100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

On 03/02/2017 11:29 AM, David Gibson wrote:
On Wed, Mar 01, 2017 at 08:54:14PM +0530, Nikunj A Dadhania wrote:
Use the softfloat api for fused multiply-add. Also, generate VXISI using
a helper function by computing intermediate result.

Um.. I really need some information on why this is a good thing to
do.  Is it a bugfix?  Enhancement? Simplification?

Looks like a bugfix to me. Previously we were attempting the operation via float128 as an intermediate type, which can result in double rounding errors.


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